NEW YORK 

 BOTanj- a;. 



PART I 

 MULTIPLE EROSION CYCLES IN PRINCIPLE 



INTRODUCTORY SKETCH 



First steps in the interpretation of the erosional histories 

 of regions were taken when (1) the processes of land de- 

 gradation by streams were worked out, (2) the limits of 

 change were recognized, and (3) the stages of reduction, 

 expressed in the terms youth, maturity, and old age were 

 described. 



Second steps were taken by Button^ who conceived that 

 the Arizona plateau had been degraded to low levels and 

 then had been uplifted in such a way as to start new cycles 

 of erosion. Following the lead of Button but bringing to 

 bear upon their studies critical and analji;ical methods 

 Willis-, Hayes and Campbell-, Davis* and others wrote his- 

 tories of parts of the Appalachian mountains, not only pre- 

 senting and explaining evidences of more than one cj^cle 

 of erosion, but working out evidences of more than two 

 cycles, describing the degree of completeness of reduction 

 reached in each cycle, giving the geologic dates of each 

 event in the erosional history of the region, interpreting 

 the number, character and dates of uplift, etc. But, by its 

 very thoroughness and accuracy, this work has led un- 

 fortunately to confusion. Later the principles so well used 

 in the Appalachian region were applied, with little con- 

 sideration, to regions where their application was doubt- 

 ful. Complex series of events were thus assigned to regions 

 whose histories were simple, and there came to be more 

 raised peneplains in literature than in the field. The care- 



er 1. Button. C. E.. "Tertiary History of the Gran.l Canyon District," U. S. Geol. 

 Cvj Surv., Monojrraph No. 2. 1SS2. 



Q^ 2. Willis, Bailey, The Northern Aijpalachians, Physiography of United States, 1S95, 

 T— pp. 169-202. 



3. Hayes. Willard C and Camijbell. M. R., "Geomorphology of the Southern Appa- 

 <0 lachians." Xat'l Geofj. Matj., Vol. VI (1S94), pp. 63-126. 

 .,_^ 4. Davis, W. M.. "Rivers and Valleys of Pennsylvania," Nat'l Geog. Mag., Vol. I 



(1889). pp. 183-253. 



